The invention relates to catalyst systems useful in hydrocarbon upgrading processes and to methods for their production and use. In another aspect, this invention relates to processes for converting oxygenated hydrocarbons to C2-C4 olefins and/or ethers, such as dimethyl ether (DME), with an increase in olefin or ether selectivity and a reduction in coke formation resulting from the conversion of such oxygenated hydrocarbons in the presence of such catalyst systems. The term xe2x80x9coxygenated hydrocarbonsxe2x80x9d as employed herein comprises hydrocarbons containing aliphatic moieties such as, but not limited to, alcohols, halides, mercaptans, sulfides, amines, ethers, and carbonyl compounds (aldehydes, ketones, carboxylic acids and the like) or mixtures thereof.
It is known to convert oxygenated hydrocarbons to olefins and/or ethers in the presence of catalysts which contain a silicoaluminophosphate (SAPO), as is described in U.S. Pat. Nos. 4,861,938; 5,475,182; 5,248,647 and 5,663,471, the disclosures of each are incorporated herein by reference.
One concern with the use of SAPO catalysts in the conversion of oxygenated hydrocarbons to olefins and/or ethers is the excessive production of coke during the conversion reaction. Coke formed during the SAPO catalyzed conversion of oxygenated hydrocarbons tends to cause catalyst deactivation. It is desirable to improve processes for the conversion of oxygenated hydrocarbons to olefins and/or ethers by minimizing the amount of coke formed during such processes. It is also desirable to have a SAPO catalyst that is useful in producing significant quantities of olefin and/or ether conversion products.
It is an object of this invention to provide an improved SAPO material which when used in the conversion of oxygenated hydrocarbons results in increased olefin yield and decreased coke production.
A further object of this invention is to provide a method for making an improved SAPO material having such desirable properties as providing for increased olefin yield and decreased coke production when used in the conversion of oxygenated hydrocarbons.
Another object of this invention is to provide an improved process for the conversion of oxygenated hydrocarbons in which the yield of olefins is increased and the production of coke is decreased.
Yet another object of this invention is to provide an improved SAPO material which when used in the conversion of oxygenated hydrocarbons results in increased ether yield and decreased coke production.
A yet further object of this invention is to provide a method for making an improved SAPO material having such desirable properties as providing for increased ether yield and decreased coke production when used in the conversion of oxygenated hydrocarbons.
Yet another object of this invention is to provide an improved process for the conversion of oxygenated hydrocarbons in which the yield of ether is increased and the production of coke is decreased.
The inventive catalyst system comprises a SAPO impregnated with a compound selected from the group consisting of phosphoric acid, boric acid, tributyltin acetate, and combinations of any two or more thereof. The inventive catalyst system can be prepared by impregnating the SAPO, under suitable conditions, with such compound. The inventive catalyst system can be used in the conversion of an oxygenated hydrocarbon to olefins and/or ethers by contacting, under conversion conditions, a hydrocarbon feedstock with the inventive catalyst system.
Other objects and advantages of the invention will become apparent from the detailed description and the appended claims.
The SAPO material used in preparing the inventive catalyst system can be any SAPO that is effective in the conversion of oxygenated hydrocarbons to olefins and/or ethers when contacted under conversion conditions with oxygenated hydrocarbons.
SAPO catalysts exhibit properties of both aluminosilicate zeolites and aluminophosphates. The SAPO""s have a three-dimensional microporous crystal framework structure of PO2, AlO2 and SiO2 tetrahedral units. The chemical composition (anhydrous) is:
mR:(SixAlyPz)O2
wherein xe2x80x9cRxe2x80x9d represents at least one organic templating agent present in the intracrystalline pore system: xe2x80x9cmxe2x80x9d represents the moles of xe2x80x9cRxe2x80x9d present per mole of (SixAlyPz)O2 and has a value of from zero to 0.3, the maximum value in each case depending upon the molecular dimensions of the templating agent and the available void volume of the pore system of the particular SAPO species involved, and xe2x80x9cxxe2x80x9d, xe2x80x9cyxe2x80x9d and xe2x80x9czxe2x80x9d represent the mole fractions of silicon, aluminum and phosphorus, respectively.
Examples of such templating agents include, but are not limited to, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide. Further details relating to the formation of SAPO compositions, including molar amounts of each oxide source, can be found in the Lok et al. U.S. Pat. No. 4,440,871, the entire disclosure of which is expressly incorporated herein by reference.
SAPO compositions useful in the present invention include, but are not limited to, SAPO-4, SAPO-5, SAPO-11, SAPO-16, SAPO-17, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-37, SAPO-40, SAPO-41, SAPO-42, and SAPO-44. The presently more preferred SAPO is SAPO-34.
The SAPO can be combined or mixed with a binder material in a liquid such as water or a hydrocarbon, by any means known to one skilled in the art such as stirring, blending, kneading, or extrusion, following which the resulting mixture can be dried in air at a temperature in the range of from about 20xc2x0 C. to about 125xc2x0 C., for a time period in the range of from about 0.5 hour to about 4 hours under any pressures that accommodate the temperatures, preferably atmospheric pressure.
Any binders known to one skilled in the art for use with a SAPO are suitable for use herein. Examples of suitable binders include, but are not limited to, aluminas such as for example xcex1-alumina and xcex3-alumina; silicas; alumina-silica; aluminum phosphate; aluminum chlorohydrate; clays such as kaolinite, halloysite, vermiculite, chlorite, attapulgite, smectite, montmorillonite, illite, saconite, sepiolite, palygorskite, and combinations of any two or more thereof. Because these binders are well known to one skilled in the art, descriptions of which are omitted herein. The presently preferred binder, if employed, is silica.
The SAPO, or SAPO-binder mixture, can be extruded into pellets or tablets by any method known to those skilled in the art.
The SAPO, whether bound in a SAPO-binder mixture, and whether or not extruded, can be impregnated with a compound selected from the group consisting of phosphoric acid, boric acid, tributyltin acetate, and combinations of any two or more thereof, by any suitable means or method known in the art for impregnating such compounds into a substrate material to thereby form an impregnated SAPO.
It is preferred to use any standard incipient wetness technique for impregnating the SAPO with such compound. A preferred method uses a liquid impregnation solution containing the desirable concentration of the compound. The concentration of the compound in the impregnation solution is generally in the range of from about 0.01 to about 10 mole percent, preferably from about 0.05 to about 7 mole percent, and most preferably from 0.1 to 5 mole percent, based on the total moles of the solution.
When the compound is phosphoric acid or boric acid it is particularly desirable to use an aqueous solution formed by dissolving the compound in water. When the compound is tributyltin acetate it is particularly desirable to use a solution formed by dissolving the tributyltin acetate in a hydrocarbon solvent, such as in a C6 to C10 cycloalkane, benzene, toluene, ethylbenzene, xylene(s), and the like. The presently preferred solvent for tributyltin acetate is cyclohexane.
The weight percent of the compound present in the impregnated SAPO is generally in the range upwardly to about 20 weight percent, preferably from about 0.01 to about 15 weight percent, and most preferably from 0.1 to 10 weight percent, based on the total weight of the impregnated SAPO.
The impregnated SAPO, whether impregnated with phosphoric acid, boric acid or tributyltin acetate, can be calcined by any suitable means or method known in the art whereby it is exposed to an atmosphere of inert gas, air or combinations thereof, under temperature and pressure conditions and for a period of time that suitably provide a calcined impregnated SAPO such that at least a portion of the metal present in the compound impregnated into the SAPO is converted to a metal oxide form.
The calcination temperature is generally in the range of from about 200xc2x0 C. to about 1000xc2x0 C., preferably from about 300xc2x0 C. to about 750xc2x0 C., and most preferably from 350xc2x0 C. to 650xc2x0 C., the calcination pressure is generally in the range of from about 0 to about 50 atmospheres (atm), preferably from about 0.1 to about 30 atm, and most preferably from 0.5 to 10 atm. The calcination can be performed in either an air atmosphere or an inert atmosphere or a combination thereof for a time period in the range of from about 0.1 hour to about 30 hours, preferably from about 2 hours to about 20 hours, and most preferably from 3 hours to 15 hours.
Any suitable hydrocarbon feedstock, which comprises oxygenated hydrocarbons, can be used as the feed to be contacted with the inventive catalyst system under suitable process conditions for obtaining a reaction product comprising olefins and/or ethers. The aliphatic moieties of the oxygenated hydrocarbons preferably contain in the range of from about 1 to about 10 carbon atoms, and more preferably, contain from about 1 to about 4 carbon atoms. Representative oxygenated hydrocarbons include, but are not limited to, lower straight or branched chain alcohols, their unsaturated counterparts and the nitrogen, halogen and sulfur analogues of such. Examples of suitable compounds include, but are not limited to, methanol, isopropanol; n-propanol; ethanol; fuel alcohols; methyl mercaptan, methyl sulfide; methyl amine, dimethyl ether (for olefin production); ethyl mercaptan; ethyl chloride; diethyl ether; methylethyl ether; formaldehyde; dimethyl ketone; acetic acid; n-alkyl amines; n-alkyl halides and n-alkyl sulfides wherein the n-alkyl groups contain 3 to 10 carbon atoms; and mixtures of any two or more thereof. The presently preferred oxygenated hydrocarbon is methanol.
The hydrocarbon feedstock can be contacted, by any suitable manner, with the inventive catalyst system described herein contained within a reaction zone which will provide the desired decrease in coke production and/or the desired conversion to olefins and/or ethers. The contacting step can be operated as a batch process step or, preferably, as a continuous process step. In the latter operation, a solid catalyst bed or a moving catalyst bed or a fluidized catalyst bed can be employed. Any of these operational modes have advantages and disadvantages, and those skilled in the art can select the one most suitable for a particular feed and catalyst.
The contacting step is preferably carried out within a conversion reaction zone, wherein is contained the inventive catalyst system, and under reaction conditions that suitably promote the formation of olefins and/or ethers from at least a portion of the oxygenated hydrocarbons of the hydrocarbon feedstock. The reaction temperature of the contacting step is generally in the range of from about 200xc2x0 C. to about 800xc2x0 C., preferably from about 250xc2x0 C. to about 750xc2x0 C. and, most preferably, from 300xc2x0 C. to 700xc2x0 C. The contacting pressure can generally range from about 0 psig to about 500 psig, preferably, from about atmospheric pressure to about 450 psig and, most preferably, from atmospheric pressure to 400 psig.
The flow rate at which the hydrocarbon feedstock is charged to the conversion reaction zone is such as to provide a weight hourly space velocity (xe2x80x9cWHSVxe2x80x9d) in the range of from about 0.01 hourxe2x88x921 upwardly to about 1000 hoursxe2x88x921. The term xe2x80x9cweight hourly space velocityxe2x80x9d, as used herein, shall mean the numerical ratio of the rate at which a hydrocarbon feedstock is charged to the conversion reaction zone in pounds per hour divided by the pounds of catalyst contained in the conversion reaction zone to which the hydrocarbon is charged. The preferred WHSV of the feed to the conversion reaction zone or contacting zone can be in the range of from about 0.25 hourxe2x88x921 to about 250 hoursxe2x88x921 and, most preferably, from 0.5 hourxe2x88x921 to 100 hoursxe2x88x921.
The process is generally carried out in the presence of one or more inert diluents which can be present in an amount in the range of from about 1 to about 99 molar percent, based on the total number of moles of all feed and diluent components fed to the reaction zone. Suitable diluents include, but are not limited to, helium, argon, nitrogen, carbon monoxide, carbon dioxide, hydrogen, water, paraffins, hydrocarbons (such as methane and the like), aromatic compounds, and mixtures of any two or more thereof. The presently preferred diluent is water.
As a further embodiment of the present invention, when the compound is phosphorous, it has been unexpectedly found that contacting the hydrocarbon feedstock with the inventive catalyst system preferentially produces either olefins or ethers, depending on the concentration of phosphoric acid in the impregnating solution (described above).
The reaction product produced from contacting the hydrocarbon feedstock with the inventive catalyst system preferentially comprises at least one olefin when the SAPO impregnation, as described above, includes a solution comprising phosphoric acid present in the solution in the range of from about 0.5 to less than about 10 weight percent (about 0.1 to less than about 2.2 mole percent), preferably from about 0.8 to about 7 weight percent (about 0.2 to about 1.5 mole percent), and most preferably from 1 to 5 weight percent (0.2 to 1.1 mole percent), based on the total weight or moles of the solution, respectively.
The impregnated SAPO can be calcined, as described above, prior to contact with the hydrocarbon feedstock.
The reaction product produced from contacting the hydrocarbon feedstock with the inventive catalyst system preferentially comprises at least one ether, preferably DME, when the SAPO impregnation, as described above, includes a solution comprising phosphoric acid present in the solution in the range of from about 10 to about 40 weight percent (about 2.2 to about 8.8 mole percent), preferably from about 12 to about 35 weight percent (about 2.6 to about 7.7 mole percent), and most preferably from 15 to 30 weight percent (3.3 to 6.6 mole percent), based on the total weight or moles of the solution, respectively.
The impregnated SAPO can be calcined, as described above, prior to contact with the hydrocarbon feedstock.